1. Field of the Invention
This invention concerns an automatic radioactivity measurement method and its apparatus in an efficiency tracing method of a liquid scintillation measurement.
2. Description of the Prior Art
The liquid scintillation counter presently in use has been developed for measuring the radioactivity of only .sup.3 H and .sup.14 C, and the radioactivity measurement method for these radionuclides is already accomplished. Besides, we have an efficiency tracing method which is effected to find the radioactivities for many kinds of radionuclides by using the liquid scintillation counter. (reference book: "Liquid Scintillation Measurement Method" by H. Ishikawa p. 159, Nanzando (1981); reference paper: M. Takiue and H. Ishikawa, "Nuclear Instrument and Method" 148, 157 (1978)).
With the efficiency tracing method it is possible to obtain the radioactivities of almost all pure beta- and beta-gamma emitters. However, the conventional efficiency tracing method has the following drawbacks, because it is manually performed. Therefore, it is currently of no practical use.
(1) Constant attention has to be paid to change manually the measurement conditions several times, while samples are measured.
(2) The selection of the best measurement region is not easy.
(3) In carrying out the efficiency tracing method, the relation between several counting efficiencies of the standard sample and the several counting rates of the subject sample is manually plotted on a graphic paper, as shown in FIG. 1, to find an extrapolated value (i.e. radioactivity of the subject sample) through drawing an efficiency tracing curve. Therefore, it is very time-consuming to perform this procedure.
(4) An accurate graph can't always be obtained, because of manual drawing.
(5) Since the error calculation for the efficiency tracing method is much more complicated than that in any other methods, the error of radioactivity is not actually determined. Thus the conventional efficiency tracing method by manual operation seems to be uncompleted as a measurement method of radioactivity.
The purpose of this invention is to provide an automatic efficiency tracing method which eliminates the drawbacks of the conventional method, and its apparatus.